The present invention relates generally to sensing of irrigation status in crops.
Water stress is known to be a major factor affecting crop yield. Further, it has long been known that crop canopy temperature is a good indicator of water stress in plants. For example, U.S. Pat. No. 4,998,826 to Wood et al., which discloses an xe2x80x9cAgricultural Infrared Thermometer,xe2x80x9d teaches (col. 1, lines 16-19) that xe2x80x9cthere is a narrow foliage temperature range, or a thermal kinetic window, within which the plant will achieve optimum yield and biomass production.xe2x80x9d
A detailed overview of the state of the art in the use of thermal infrared measurements for monitoring and measuring plant health may be found in xe2x80x9cThermal Infrared Measurement as an Indicator of Plant Ecosystem Healthxe2x80x9d (520-670-6380 X 171, June 2000) by M. Susan Moran, published by USDA-ARS Southwest Watershed Research Center, Tucson, Ariz.
It is also known that the difference in temperature between well-watered and inadequately watered or stressed crop canopies depends on additional environmental factors such as total incident radiation, air temperature, relative humidity, and wind speed. In their article, xe2x80x9cCanopy Temperature Characterization of Corn and Cotton Water Status,xe2x80x9d Transactions of the ASAE, 43(4), 867, the contents of which are incorporated herein by reference, Wanjura and Upchurch review the progression of different measures of crop water stress and how they are determined or calculated and conclude that the crop water stress index (CWSI) is a superior measure of water stress, but that both theoretical and empirical forms of the CWSI (CWSI-T and CWSI-TC, respectively) require measurement or calculation of multiple environmental factors that make their application difficult and impractical.
U.S. Pat. Nos. 4,755,942 and 4,876,647 to Gardner et al. disclose portable apparatus to determine crop water stress by simultaneously measuring a number of environmental and plant physiological parameters including air temperature, relative humidity, and plant canopy temperature. However, measurements with the apparatus disclosed therein have the limitations of variations in the environmental parameters over time and across the extent of typical crop-growing areas and variations in plant canopy temperature measurements as a result of differences in the position and orientation of a hand-held sensor. As a result, the determination of crop water stress with the disclosed system is of limited reliability. Further, given the size and non-uniformity of typical crop-growing areas, measurements with the hand-held apparatus disclosed therein are totally impractical except for spot-checking, as opposed to systematic monitoring of plant water stress desired in commercial agriculture.
Another approach is that of Murray in U.S. Pat. No. 5,710,047, xe2x80x9cMethod for Monitoring Growth and Detection of Environmental Stress in Plants,xe2x80x9d which relies on laboratory analysis of sample plant tissues. The method disclosed therein, while accurate, is also impractical for the systematic monitoring desired in commercial agriculture, especially if it is desired to control irrigation of crop-growing areas in a timely manner.
The present invention seeks to provide a method and system for evaluating the water stress status of growing crops in nearly real time employing remote monitoring of entire crop-growing areas, rather than sampling or spot checks, at sufficiently high resolution to recognize features in the crop-growing area, especially to distinguish between crop foliage and non-foliage features, and requiring minimal additional measurements of environmental parameters in the crop-growing area.
There is thus provided, in accordance with a preferred embodiment of the invention, a system for evaluating the water stress status of growing crops including:
a reference array near or within a selected crop-growing area for performing reference parameter measurements thereon;
one or more sensors, which may be portable, for measuring environmental parameters, such as global radiation, air temperature, relative humidity, and wind speed, in the vicinity of the crop-growing area and of the reference array;
a portable imaging sensor for measuring a preselected physical parameter, preferably surface temperature, on a pixel by pixel basis over a selected area, thereby producing a two-dimensional array of pixels corresponding to a thermal image of the crop-growing area and of the reference array;
a portable location sensor for detecting global location reference signals;
a mobile platform, preferably airborne, for supporting all the portable sensors, which maintains a predetermined altitude during measurement by the portable imaging sensor so that the thermal image of the crop-growing area and of the reference array is made up of measurement pixels of a predetermined size, preferably providing a measurement of the surface temperature of an area smaller than a meter squared;
data processing apparatus, which may also include one or more data storage devices, arranged in data receptive association with each other and with the sensors for receiving parameter measurements therefrom; and
a multiplicity of communications devices for transmitting the parameter measurements from the sensors and data storage devices to the data processing apparatus;
wherein the reference array allows measurement of reference parameters which, together with crop parameter measurements of growing crops, facilitates the data processing apparatus in determining the water stress status of the growing crops.
Additionally in accordance with a preferred embodiment of the invention, there is provided for use with the system for evaluating the water stress status of growing crops, a reference array near or within a selected crop-growing area for performing reference parameter measurements thereon, which includes a plurality of component reference surfaces, typically formed of fabric, in a predetermined arrangement, each of the component reference surfaces being a predetermined size and having predetermined radiometric and heat-convection properties; and wherein the component reference surfaces allow measurement of a plurality of reference parameters which, together with crop parameter measurements of growing crops, facilitates determination of the water stress status of the growing crops. The component reference surfaces include one or more first reference surfaces fabricated to produce preselected parameter measurements substantially equivalent to those taken on a potentially transpiring crop surface that is internally saturated and one or more second reference surfaces, which are substantially dry, shielded from thermal radiation coming from therebelow, and fabricated to have predetermined heat-convection properties. Accordingly, the first reference surface is configured to permit substantially free evaporation therefrom and includes wetting apparatus which continuously wets ARS 15 first reference surface with water during preselected time intervals including when measurements are to be taken. Further in accordance with a preferred embodiment of the invention, there are two or more second reference surfaces, which are substantially dry and which include one or more uniformly light-colored surfaces and one or more uniformly dark-colored surfaces.
In accordance with an alternative embodiment of the invention, the reference array may further include one or more environmental sensors for measuring predetermined environmental parameters at its location. Additionally in accordance with an alternative embodiment of the invention, the reference array may also include temperature sensors for measuring the surface temperatures of the component reference surfaces of the reference array. The reference array may also include a clock device for producing time reference signals and wireless transmission apparatus for transmitting reference parameter measurements and time reference signals to the system so that the system can synchronize the reference parameter measurements with crop parameter measurements for determination of the water stress status of the growing crops. Alternatively, the reference array may further include a data storage device for storing all measurements until they are transmitted by the wireless transmission apparatus to the system for processing.
In accordance with a preferred embodiment of the invention, the size of the component reference surfaces of the reference array allows them to correspond to a predetermined number of whole pixels, preferably, at least four, in the thermal image of the crop growing area and of the reference array produced by the portable imaging sensor when performing measurements at the predetermined altitude above of the crop growing area and of the reference array.
In accordance with yet a further preferred embodiment of the invention, there is provided a method for evaluating the water stress status of growing crops employing the system and the reference array described hereinabove. The method includes the steps of:
providing, near a selected crop-growing area, a reference array, with a number of component reference surfaces, for reference parameter measurements;
measuring, in the vicinity of the crops and in the vicinity of the reference array, a plurality of measurements of a predetermined set of environmental parameters, such as global radiation, air temperature, relative humidity, and wind speed;
measuring, for the crops and for the reference array, a plurality of measurements of a predetermined set of physical parameters, preferably of the surface temperature, wherein each measurement includes a physical parameter measurement and the location at which the physical parameter was measured;
identifying, by means of the location measurement associated with each physical parameter measurement, those measurements of physical parameters pertaining to the component reference surfaces of the reference array, and those measurements of physical parameters pertaining to the crop-growing area; and
employing the measured parameters for the crop-growing area and those for the reference array for evaluating the water stress status of the crops growing in the crop-growing area.
The step of providing a reference array, includes providing wet component reference surfaces and wetting them with water continuously during preselected time intervals including intervals when measurements are to be taken, and providing dry component reference surfaces, as described hereinabove.
Additionally in accordance with a preferred embodiment of the invention, the step of measuring a plurality of measurements of the surface temperature includes the step of imaging the crop-growing area and the reference array from a predetermined altitude, preferably from an airborne platform, with a thermal imaging radiometer thereby producing a two-dimensional array of pixels corresponding to a thermal image of the crop-growing area and the reference array wherein each pixel of the thermal image provides a measurement of the surface temperature of an area of a preselected size, preferably smaller than a meter squared, of the crop-growing area. The step of imaging may include the substeps of:
producing a number of partial images of the crop-growing area;
locating, to a preselected precision, each of the partial images of the crop-growing area, preferably by measuring a global location reference signal for each partial image; and
splicing the partial images of the crop-growing area to produce a two-dimensional array of pixels corresponding to a thermal image of the entire crop-growing area and of the reference array.
Further, in accordance with a preferred embodiment of the invention, the component surfaces of the reference array will each correspond to a predetermined number of pixels, preferably at least four, in the thermal image produced in the step of imaging.
Additionally in accordance with a preferred embodiment of the invention, the step of identifying further includes the step of distinguishing the pixels in the thermal image of the crop-growing area corresponding to locations covered with crop foliage from the pixels in the thermal image of the crop-growing area corresponding to locations not covered with crop foliage.
In accordance with a preferred embodiment of the invention, the step of employing the measured parameters includes the steps of:
performing statistical analysis of the pixel measurements for a predetermined subset of the pixels in the thermal image of the crop-growing area corresponding to areas covered with crop foliage, thereby determining an effective crop canopy temperature Tc;
determining, from the pixel measurements corresponding to all the component reference surfaces of the reference array and from the measurements of the environmental parameters, preferably from the measurements of the global radiation, in the vicinity of the reference array, the theoretical maximum and minimum crop canopy temperatures, Tmax, and Tmin, respectively;
calculating the crop water stress index (CWSI) for the crop-growing area using the formula:
{CWSI}=(Tcxe2x88x92Tmin)/(Tmaxxe2x88x92Tmin);
and evaluating the water stress status of the growing crops from the crop water stress index for the crop-growing area.
In accordance with an alternative embodiment of the invention, the step of determining is performed from the pixel measurements corresponding to the first, or wet, component reference surface of the reference array and from the measurements of the air temperature in the vicinity of the reference array.
In accordance with still another alternative embodiment of the invention, the step of measuring a plurality of measurements of a predetermined set of physical parameters further includes the steps of:
measuring a global location reference signal for the reference array;
measuring a plurality of measurements of the surface temperature for all the component reference surfaces of the reference array by means of surface temperature sensors associated with the reference array, as described hereinabove; and
synchronizing, by means of the clock and the wireless transmission apparatus associated with the reference array, as described hereinabove, the measurements of the surface temperature for all the component reference surfaces of the reference array with the plurality of measurements of the surface temperature for the crops.
Thus, in accordance with a preferred embodiment of the invention, the step of determining is performed from the synchronized temperature measurements corresponding to all the component reference surfaces of the reference array measured by the sensors associated therewith and from the measurements of the global radiation in the vicinity of the reference array. In accordance with an alternative embodiment of the invention, the step of determining is performed from the synchronized temperature measurements corresponding to the first, wet, reference surface of the reference array measured by the sensors associated therewith and from the measurements of the air temperature in the vicinity of the reference array.